Field of Invention
The present invention relates to a semiconductor process, and more particularly to a method of forming a contact structure.
Description of Related Art
MOS is a basic structure widely applied to various semiconductor devices, such as memory devices, image sensors and display devices. An electric device is required to be made lighter, thinner and smaller. The traditional MOS transistor is difficult to scale down due to the limitation of the fabricating process, and a multi-gate transistor with better properties is therefore developed.
In either a traditional MOS transistor or a multi-gate transistor, the aspect ratio of a contact opening becomes larger and larger as the device size is continuously scaled down. Complicated steps are usually implemented to form a high-aspect-ratio contact structure, and the process cost is thereby increased.